Treatment of derivatives of cellulose



Patented Mar. 1, 1938 TREATMENT OF DERIVATIVES OF CELLULOSE George Schneider, Montclair, N. J., assignor to Celanese Corporation tion of Delaware of America, a corpora- No Drawing. Application February 24, 1936-,

- Serial No. 65,417

6 Claims.

This invention relates to derivatives of cellulose and relates more particularly to the treatment of organic esters of cellulose to reduce their corrosive properties and color and increase their clarity characteristics.

This application is a continuation in part of my application S. No. 49,555, filed November 13, 1935.

An object of my invention is to treat derivatives of cellulose, particularly organic esters of cellulose with chlorine or chlorine liberating agents to improve their properties. Another object of my invention is to treat organic esters of cellulose with solutions of chlorine or hypochlorites whereby the corrosive properties of'the organic esters of cellulose are reduced. Other objects of my invention will appear from the following detailed description.

Organic derivatives of cellulose, such as cellulose acetate, as ordinarily made contain certain colored constituents or ingredients that tend to impair their usefulness in the making of plastics, films, filaments and the like, particularly where transparency and freedom from color are desired. Thus, when a thick sheet or block of a plastic composition containing such derivatives of cellulose is made, the same has a distinct greenish brown color and is of poor transparency.

Organic derivatives of cellulose, such as cellulose acetate, as ordinarily made also contain certain constituents or ingredients that tend to corrode metallic machine elements and parts of filament-spinning and plastic working devices. For instance, in spinning a solution of cellulose acetate dissolved in a volatile solvent by extruding the same through suitable orifices into an evaporative or precipitating medium, the solutions containing the cellulose acetate as normally made tend to corrode the jet holes or orifices. If the corroded material remains in the jet hole, there is produced a filament having a denier below that desired, while if the corroded material is broken away from the jet hole the jet hole is enlarged, thus producing a filament having a greater denier than that desired and of undesirable cross-section. It has been the practice heretofore to frequently change the spinning jets and to make periodic examination as to their condition. This interrupts spinning. Moreover, jet replacements are costly. Furthermore, if improper inspection is made or the jets are not replaced frequently there is produced a yarn which is not uniform as to denier, cross-section, etc. This non-uniformity of the yarn reflects in the fabric produced from the same, sometimes making a second quality fabric.

I have found that if derivatives of cellulose, and particularly organic derivatives of cellulose,

are subjected to the action of a hypochlorite'or f other chlorine liberating agent prior to being precipitated from the solution in which they are formed, a large proportion of the color imparting and corrosive constituents are either destroyed or are converted into compounds that tend to produce such objectionable action to a lesser extent.

In accordance with my invention, I prepare derivatives of cellulose, and especially organic esters of cellulose, of reduced corrosive properties and of reduced color, which organic derivatives of cellulose are capable of producing products of greater transparency, by subjecting the organic derivative of cellulose, while in solution, to the action of chlorine. Preferably, the solution of organic derivative of cellulose that is subjected to chlorine water or a hypochlorite or other chlorine liberating material is the solution in which the organic derivative of cellulose is formed or this solution after an additional amount of solvent or diluent has been added.

While other derivatives of cellulose, such as cellulose nitrate and cellulose ethers,. may be treated in accordance with this invention, I prefer to treat organic acid esters of cellulose, examples a of which are cellulose acetate, cellulose formate, cellulose propionate and cellulose butyrate.

The organic derivative of cellulose may be formed by any suitable method. For instance, cellulose acetate may be. formed by treating cellulose With acetic anhydride in the presence of a catalyst and a suitable diluent or solvent such as 1 acetic acid. The cellulose acetate thus formed may be subjected to a hydrolysis or ripening treatment to produce the desired solubility characteristics therein. The ripening or hydrolysis may be performed by allowing the cellulose acetate still dissolved in the liquors formed during esterification to stand for a period of time at suitable temperatures. By this process cellulose acetate which when formed is soluble in chloroform may be made soluble in acetone. The other esters of cellulose may be formed in a similar manner. For the purpose of describing this invention and in the appended claims, the term primary solution refers to a solution of cellulose ester in the solvent produced or added during the esterification of thecellulose. For instance, the primary solution of cellulose acetate, as formed in accordance with the above description, is the acetic acid solution of cellulose acetate containing some sulphuric acid.

Although I have found that satisfactory results may be obtained by treating the derivatives of cellulose with chlorine or a solution of a hypochlorite by adding the same to the esterification mixture before or during the hydrolysis and ripening steps, I prefer to treat the derivatives of cellulose, while in the primary solution, at the end of the hydrolysis or ripening step and after thinning the said solution by the addition of a weak acid corresponding to the organic acid in the primary solution. Thus, the primary solution of cellulose acetate may have added thereto chlorine or a hypochlorite solution immediately prior toor during the precipitation of the cellulose acetate from the solution. The precipitating step may be effected by adding to the primary solution of cellulose acetate a solution of an alkali carbonate or an alkali acetate or other alkali salt of a fatty acid in a quantity sufiicient to neutralize the catalyst, then adding water until the material is precipitated. The inorganic salts and other water soluble matter may be washed from the precipitated cellulose acetate. It is during this precipitating step that I prefer to subject the cellulose acetate to the action of chlorine. However, I prefer to first thin the solution by the addition of a weak acetic' acid. The chlorine or hypochlorite solution may be added to the primary solution prior to the addition of the alkali carbonate or acetate, or the hypochlorite solution may be added concurrently therewith. However, the hypochlorite solution should be added before the addition of the large amount of water used in precipitating the cellulose acetate. In like manner, the other organic esters and ethers of cellulose may be subjected to the hypochlorite treatment.

Although the chlorinating agent may be applied to the primary solution of cellulose acetate in any suitable manner, I prefer first to thin the primary solution of the cellulose acetate by adding thereto an amount of dilute organic acid such that precipitation is just about to take place. For instance, in the production of cellulose acetate formed in an acetic acid solvent, dilute acetic acid may be added to the material just prior to precipitation such that a very thin solution of the organic derivative of cellulose and acetic acid is formed. The concentration of the dilute acetic acid may be such that a sufiicient thinning of the solution may be obtained without requiring a substantial increase in the amount of water required for precipitation. To this thinned solution the chlorine or chlorine liberating material may be added preferably while agitating the same. If other solvents than acetic acid are employed in the primary solution, the addition of that solvent or that diluent may be added prior to the chlorinating agent to make a relatively thin solution of the organic derivative of cellulose.

Chlorine, chlorine water or any suitable hypochlorite may be employed in the process or my invention, examples of which are the hypochlorites of sodium, potassium, calcium or magnesium. The chlorine, chlorine Water or the hypochlorite is applied preferably in an aqueous solution and in a suitable concentration and quantity to supply from .02 to 1% by weight on the derivative of cellulose of available chlorine. The time of treatment is as required, say, from 1 minute to 3 hours or more, depending on the concentration of the hypochlorite solution, the

relative action of the same on the cellulose derivative and the condition of and chemicals contained in the primary solution of the cellulose derivative. In order to effect a rapid and high degree of chlorination, the temperature of the treatment may be raised to above that of room temperature, say, from 24 to C. However, this is not necessary and successful results are 7 obtained even at temperatures below room temperature.

Cellulose derivatives that have been treated with chlorine or a hypochlorite solution at the end of the ripening or hydrolysis period and then precipitated, may have a lighter color imparted thereto by subjecting the same in the precipitated' form to a bleaching treatment. This latter treatment tends to form a derivative of cellulose that is more clear, particularly when formed into a sheet or block. The treatment of the solution of the cellulose derivative with that have no -pigments or dyes or for the making of light colored plastics. However, the derivative of cellulose produced by my process may be employed for making dark colored materials.

The derivative of cellulose, when treated by my process, may be formed into sheets and films by casting the same on film-forming wheels and belts formed of metal alloys without corroding the same. Films formed of a corrosive derivative of cellulose tend to take on a color or absorb the discolored products of corrosion from the film casting belt or wheel. This property is obviated from the derivative of. cellulose produced in accordance With my invention and such derivatives of cellulose in a volatile solvent therefor may be spun into filaments through spinning jets made of metal alloys with substantially no corrosive action on the spinning jets. Thus, a cellulose derivative produced in accordance with my invention forms more uniform filaments,

yarns, straws, etc. than those made of untreated derivatives of cellulose. The spinning into filaments or yarns of organic derivatives of cellu lose, treated in accordance with my invention, is also more economical than the spinning of untreated derivatives of cellulose in that the periods of inspection of the jet orifices may be less frequent and the replacing of jets substantially eliminated.

The derivative of cellulose treated in accordance with my invention may also be associated with volatile solvents therefor, and also plasticizers such as triacetin, diethyl tartrate, dibutyl tartrate, diethyl phthalate, triphenyl phosphate, or other suitable plasticizers by any known processes, to form plastic sheets, blocks, tubes, rods or articles by any suitable process. Another important application of this invention is in the making of molding powders containing a purified derivative of cellulose in finely divided condition in association with plasticizers but containing little or substantially no volatile solvents, which molding powders may be molded under heat and pressure to the desired shape. Films to be employed as a base for photographic or cinematographic filmsor' for other purposes may also be made from this material. The purified derivative of cellulose may also be used for making lac-.

quers, particularly clear or light colored lacquers. The derivatives of cellulose made in accordance with this invention being substantially non-corrosive, are particularly suitable for use where solutionsof the same in volatile solvents are caused to repeatedly or continuously contact with the same metal surfaces.

The organic esters of cellulose may be treated with chlorine or the chlorine liberating material while in any suitable solution. The best results, however, are obtained upon treating the organic ester in the primary solution after hydrolysis. When treating the organic esters with chlorine prior to hydrolysis the percentage of chlorites in the resulting material is increased, whereas the treatment of the organic derivative or cellulose withchlorine after hydrolysis produces a comparatively small amount of chlorites and upon washing and stabilizing the material has no trace of free chlorine. This freedom from. chlorites and free chlorine is essential to the production of an organic ester of cellulose having good stability.

In order further to illustrate my invention but without being limited thereto, the following specific examples are given:

Example I A solution of cellulose acetate, which is formed by reacting cellulose with acetic anhydride in the presence of sulphuric acid as a catalyst and acetic acid as a solvent diluent, has water added thereto and is ripened or hydrolyzed until the cellulose acetate is soluble in acetone.

The resulting solution may comprise, for instance, 500 parts by weight of cellulose acetate, 1,600 parts by weight of acetic acid (93% concentration) and 50 parts by weight of sulphuric acid (98% concentration) and is in the form of a heavy viscous syrupy solution. This material is placed in a device capable of mixing or whipping the material and then about 500 parts by weight of Weak acetic acid (70% concentration) is added. A freshly prepared concentrated aqueous solution or slurry of 85.5 parts by weight of sodium bicarbonate is thoroughly beaten into the solution to form a creamy mass. After beating in the sodium bicarbonate there is added sufiicient chlorine water such that there is present 0.1%, on the weight of the cellulose acetate, of chlorine. The mass is whipped for from 5 to 15 minutes.

Thereupon warm water is slowly added to the mass with stirring, but the amount of water added at this stage closely approaches but does not equal that required to cause precipitation of the cellulose acetate. The amount of water required for this purpose varies with the degree of hydrolysis of the cellulose acetate, the amount of water contained in the weak acid added, etc. After this, water is added in large amounts and at a fast rate with vigorous stirring of the mass, the cellulose acetate precipitates in the form of fiufiy, light fibres which may be easily washed with water to free the same of free chlorine and chlorites as well as the other inorganic salts that may have been formed. The material may then be stabilized by boiling with water containing a small amount of mineral acid such as sulphuric acid.

Example II The same procedure and proportions are employed as in Example I with the exception that a solution of a hyprochlorite is substituted for the chlorine water.

Example III ployed. In general terms, it may be stated that the amount of weak acid is sufficient to materially thin the solution of the organic ester of cellulose without causing precipitation.

The cellulose acetate treated in accordance with any of the above examples may be given a bleaching treatment with a chlorine liberating material or with a peroxide after said material has been precipitated. This bleaching treatment tends to reduce the color of solutions or articles made from the cellulose acetate After any of the above treatments containing chlorine or a hypochlorite, the cellulose acetate may be given an anti-chlor treatment. For instance, to every 100 parts of cellulose acetate the same may be. treated with 0.1 pound of borax dis solved in 121 gallons of water. If desired, the

anti-chlor treatment may be effected on the cellulose acetate prior to precipitation in the processes described in the examples.

The derivatives of cellulose may be formed in any suitable mannenalso any suitable percentages of catalyst, reacting acid, solvent etc. employed may be used. The sodium bicarbonate or other alkali carbonate is added for the purpose of removing the catalyst and the amount employed will, therefore, depend upon the amount of catalyst employed.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. Method of preparing an organic ester of cellulose substantially free from corrosive action, which comprises adding to a ripened esterification solution of the organic ester of cellulose a weak organic acid in amount substantially equal to the weight of the said solution, and treating the resulting solution with an agent selected from the group consisting of chlorine, chlorine Water and hypochlorites.

2. Method of preparing cellulose acetate substantially free from corrosive action, which comprises adding to a ripened esterification solution of cellulose acetate a weak organic acid in amount substantially equal to the weight of the said solution, and treating the resulting solution with an agent selected from the group consisting of chlorine, chlorine water and hypochlorites.

3. Method of preparing an organic ester of cellulose substantially free from corrosive action, which comprises adding'to a ripened esterification solution of the organic ester of cellulose a weak organic acid in amount substantially equal to the weight of the said solution,- and treating the resulting solution with an agent selected from the group consisting of chlorine, chlorine water and hypochlorites in an amount equivalent to from 0.02 to 1% of free chlorine based on the weight of the organic ester of cellulose.

4. Method of preparing celluloseacetate substantially free from corrosive action, which comprises adding to a ripened esterification solution of cellulose acetate a weak organic acid in amount substantially equal to the weight of the said solution, and treating the resulting solution with an agent selected from the group consising of chlorine, chlorine water and hypochlorites in an amount equivalent to from 0.02 to 1% of free chlorine based on the weight of the cellulose acetate.

5. Method of preparing an organic ester of cellulose substantially free from corrosive action, which comprises adding to a ripened esterification solution of the organic ester of cellulose a weak organic acid in amount substantially equal to the weight of the said solution, treating the resulting solution with an agent selected from the group consisting of chlorine, chlorine water and hypochlorites, and subjecting the treated organic ester of cellulose to a subsequent treatment with an anti-chlor.

6. Method of preparing cellulose acetate substantially free from corrosive action, which comprises adding to a ripened esterification solution of the cellulose acetate a weak organic acid in amount substantially equal to the weight of the said solution, treating the resulting solution with an agent selected from the group consisting of chlorine, chlorine water and hypochlorites in an amount equivalent to from 0.02 to 1% of free chlorine based on the weight of the cellulose acetate, and subjecting the treated cellulose acetate to a subsequent treatment with an anti-chlor.

GEORGE SCHNEIDER. 

